1. Field of the Invention
The present invention generally relates to the area of video signal encoding/decoding, more particularly to techniques for motion estimation in video signal processing.
2. Description of the Related Art
One of the key elements in video signal encoding is motion estimation. A video sequence includes a series of frames. To achieve compression, the temporal redundancy between adjacent frames can be exploited. For example, a frame is selected as a reference frame, and subsequent frames are predicted from the reference frame using a technique known as motion estimation. The frame undergoing motion estimation is called a current frame or an estimated frame. The processing of video signal encoding using motion estimation is also known as interframe compression. When using motion estimation, an assumption is made that the objects in the scene have only translational motion. This assumption holds as long as there are no sudden camera panning, zooming, changes in luminance, or rotational motion. Using motion estimation in interframe compression can reduce redundant frames in an encoded (i.e., compressed) video stream. As a result, a higher compression ratio can be achieved. There are a number of video signal encoding techniques and standards that use motion estimation to predict the current frame (e.g., MPEG-1, MPEG-2, MPEG-4, H.261, H.263 and H.264).
In general, about 40-70% of the total computation of a video signal encoding process is spent in motion estimation. Due to the limited computation capacities in an embedded processor, the motion estimation is often performed with the assistance of a hardware or a motion estimator (e.g., ASIC, FGPA, etc.). This arrangement reduces the computation requirement of the embedded processor. However, there is a problem associated with carrying out motion estimation in this arrangement. A large amount of data must be transmitted between the processor and the motion estimator. As a result, the system bus of a video signal decoder is overloaded and the performance suffers.
Therefore, there is a need for techniques for motion estimation that can reduce the data traffics in the system bus and improve overall performance of video signal encoding.